Method for the continuous production of aromatic carbonates

ABSTRACT

The present invention provides a method for making aromatic carbonates. In this method, an aryl alcohol is reacted with a dialkyl carbonate in a reactor (e.g., a distillation column) to produce an arylalkyl carbonate and diaryl carbonate. In one embodiment, the method comprises: feeding to the top subsection of the reactive section of a distillation column, a first stream comprising an aryl alcohol and a catalyst, and feeding to the bottom subsection of the reactive section a second stream containing a dialkylcarbonate, wherein the temperature at the bottom of the column is between 220° C. and 240° C.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 09/713,692, filed Nov. 15, 2000, which is incorporated hereinin its entirety.

BACKGROUND OF INVENTION

This application relates to the continuous production of aromaticcarbonates by reaction of dialkyl carbonates and an aromatic alcohol inthe presence of a catalyst.

Aromatic carbonates, such as diphenyl carbonate, are an importantreactant in the production of polycarbonate resins. Polycarbonate resinsare being used in an ever increasing number of applications. Therefore,the efficient production of diary carbonates has become moresignificant. Early processes for the production of diaryl carbonatesused phosgene as a reagent. However, the toxicity of phosgene promptedthe development of a non-phosgene process. As shown in FIG. 1, thisnon-phosgene process has two-steps. First, a dialkyl carbonate, such asdimethyl carbonate (DMC), reacts with an aromatic alcohol, such asphenol, to produce an alkyl aryl carbonate (e.g., phenyl methylcarbonate, PMC) and an alkyl alcohol (e.g., methanol). Next, twomolecules of the alkyl aryl carbonate undergo a transesterificationreaction to produce one molecule of diaryl carbonate (e.g., diphenylcarbonate, DPC) and one molecule of dialkyl carbonate (e.g., DMC).

Various methods and apparatus for making diaryl carbonates without usingphosgene are known in the art. For example, U.S. Pat. No. 5,210,268,which is incorporated herein by reference, relates to a process forcontinuously producing aromatic carbonates. The process is carried outin a distillation column, wherein products are recovered from the bottomof the column, and low boiling by-products are removed from the top ofthe column. Other processes for production of diaryl carbonates using aseries of distillation columns are disclosed in U.S. Pat. Nos. 5,344,954and 5,705,673.

U.S. Pat. Nos. 5,705,673; 5,344,954; 5,334,742; 4,182,726, and 5,380,908describe processes for making diaryl carbonates using apparatus whichcomprises at least two distillation columns: the first to produce phenylmethyl carbonate, and the second to convert the phenyl methyl carbonateinto diphenyl carbonate. No commercially viable apparatus has beendisclosed which is capable of producing sufficient yields of diphenylcarbonate in the first column to eliminate the necessity of a secondcolumn. A single column design would make the production process moreeconomical. Accordingly, it would be most desirable to find a processwherein the yield of PMC and DPC versus the initial phenol feed is 50%or more, and the amount of DPC produced is maximized versus the totalyield of PMC and DPC. Excess production of undesirable by-products suchas phenyl methyl ether (i.e., anisole) should also be avoided.

It was discovered the above goals may all be accomplished by the presentinvention. Specifically, it is possible to obtain a 51% yield of PMCplus DPC with a selectivity to anisole byproduct of less than 0.2%,wherein the selectivity of DPC relative to the sum of PMC and DPC was 30to 40%. The present invention therefore provides a method for continuousproduction of diphenyl carbonate which has a high production rate whileat the same time providing an energy and raw material efficient process.

SUMMARY OF INVENTION

The present invention provides a method for making aromatic carbonates.In this method, an aryl alcohol is reacted with a dialkyl carbonate in areactor (e.g., a distillation column) to produce a arylalkyl carbonateand diaryl carbonate. The total yield of arylalkyl carbonate and dialkylcarbonate together is at least 40%. Also, the selectivity of diarylcarbonate versus diaryl carbonate and arylalkyl carbonate together ispreferably at least 25%.

In the method according to the present invention, the temperaturemeasured at the bottom of the distillation column is preferably between220 and 240° C., the DMC to phenol feed ratio is preferably between 4and 7, the operating pressure measured at the top of the column isbetween 3 and 6 kg/cm² Gauge, and the amount of catalyst used ispreferably from 0.5 to 1 molar percent.

In a more specific embodiment, the present invention provides a methodfor making aromatic carbonates in a distillation column having a lowerreactive section and an upper rectification section. In this embodiment,a first reactive stream comprising an alcohol, and optionally a dialkylcarbonate and a catalyst, are fed into the top of the reactive section.A second stream containing a dialkyl carbonate, and optionally an arylalcohol are fed into the bottom of the reactive section. The two streamsare fed in sufficient quantities such that the weight ratio between thedialkyl carbonate and the aryl alcohol is from 4 to 6. The temperaturemeasured at the bottom of the column is between 220° C. and 240° C., andthe operating pressure measured at the top of the column is from 3 to 6kg/cm² Gauge.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the two-step reaction of dimethyl carbonate and phenol toproduce diphenyl carbonate.

FIG. 2 shows schematic diagram of an apparatus in accordance with theinvention.

FIG. 3 shows a graph depicting the relationship between PMC and DPCyield versus reaction temperature and DMC to phenol feed flow ratio.

FIG. 4 shows a graph depicting the relationship between anisoleselectivity versus reaction temperature and DMC to phenol feed flowratio.

FIG. 5 shows a graph depicting the relationship between DPC selectivityrelative to total yield of PMC and DPC versus reaction temperature andDMC to phenol feed flow ratio.

FIG. 6 shows a graph depicting the relationship between PMC and DPCyield together with anisole selectivity as a function of reactiontemperature and DMC to phenol feed flow ratio.

DETAILED DESCRIPTION

For purposes of the present application, the term “distillation column”shall refer to any sort of distillation column or reactive distillationcolumn in which a process of distillation may be carried out.

For purposes of the present invention, the term “reaction mixture”includes the materials fed into the distillation column, which typicallyincludes the aromatic alcohol and the dialkyl carbonate, and optimally acatalyst, arylalkyl carbonate, and other optional substances such as,for example entraining agents and/or solvents.

For purposes of the present application, the term “yield” or “totalyield” shall refer to a weight percentage of the desired product(s)(e.g., aryl alkylcarbonates and diaryl carbonates) relative to the totalweight of the mixture of products and reactant determined afterobtaining a stable continuous operation.

For purposes of the present application, the term “selectivity” in thecontext of DPC shall refer to the weight ratio of DPC over the sum ofthe products DPC and PMC.

For purposes of the present application, the term “selectivity” in thecontext of anisole content shall refer to the weight ratio of anisoleover the total weight of the mixture of products and reactantsdetermined after obtaining a stable continuous operation.

For the purposes of the present application, the term “top of thecolumn” is a relative term indicating a location within the upper ⅓ of adistillation column, which would include, but not necessarily be limitedto, a position above the uppermost plate in said column.

For purposes of the present application, the term “bottom of the column”is a relative term indicating a location within the lower ⅓ of adistillation column, which would include, but not necessarily be limitedto, a position below the lower most plate in said column.

For the purposes of the present application, the term “lowerrectification section” shall refer to a lower section of a distillationcolumn below the feeding point of at least one of the reactants whereinthe chemical reaction is thought to occur in said section.

For purposes of the present application, the term “upper rectificationsection” shall refer to an upper section of a distillation column abovethe lower rectification section, wherein the chemical reaction isgenerally thought not to occur in said rectification section.

For the purposes of the present application, the term “operatingpressure” is meant to refer to an average pressure reading during stableoperation of the reaction, which pressure may vary throughout theprocess and upon start up and shut down.

For the purposes of the present application, technical terms not definedherein should be interpreted according to Grant & Hackh's ChemicalDictionary, 5^(th) Ed., Roger Grant and Clair Grant, McGraw-Hill, Inc.,1987.

Relevant sections of all U.S. Patents referred to herein are all herebyincorporated by reference.

As shown in FIG. 1, the chemical reaction employed in the presentinvention is a reaction between an aromatic alcohol and a dialkylcarbonate. The aromatic alcohol and dialkyl carbonate should be selectedsuch that they will undergo an exchange reaction with each other. FIG. 1depicts a preferred reaction between phenol (an aromatic alcohol) anddimethyl carbonate (a dialkyl alcohol). FIG. 1 further depicts thedisproportionation of one of the arylalkyl carbonate product,phenylmethylcarbonate, to form the diaryl carbonate product, diphenylcarbonate.

Suitable aromatic alcohols which are useful in the present reactioninclude phenol and alkylphenol such as cresol, xylenol,trimethyl-phenol, tetramethylphenol, ethylphenol, propylphenol,butylphenol, diethylphenol, methylethylphenol, methylpropylphenol,dipropylphenol, methylbutylphenol, pentylphenol, hexylphenol,cyclohexylphenol, and alkoxyphenols such as methoxyphenol andethyoxyplenol. Suitable dialkyl carbonates which are useful in thepresent reaction include dimethylcarbonate, diethylcarbonate,methylethylcarbonate, ethylpropylcarbonate, dipropylcarbonate,propylbutylcarbonate, dibutylcarbonate, butylpentylcarbonate,dipentylcarbonate, pentylhexylcarbonate, dihexylcarbonate,hexylheptylcarbonate, diheptylcarbonate, heptyloctylcarbonate,dioctylcarbonate, octylnonylcarbonate, dinonylcarbonate,nonyldecylcarbonate, didecylcarbonate. It is also possible to usecombinations of two or more aromatic alcohols and/or dialkyl carbonates.

The product diarylcarbonates are useful starting materials for preparingpolycarbonates by reacting them with dihydric phenols (e.g., BisphenolA) via the melt reaction. A very early description of the melt synthesisof polycarbonates is found in U.S. Pat. No. 3,153,008, but the patentliterature is replete with further descriptions such as that found inU.S. Pat. No. 4,182,726.

Preferred classes of catalysts for conducting the reaction shown in FIG.1 include titanium compounds like titaniumtetraphenoxide (Ti(OPh)₄), andTitaniumtetrachloride, organotin compounds, lead compounds, compounds ofthe copper family metals, zinc complexes, compounds of the iron familymetals, and zirconium complexes. The catalyst selected should preferablyhave an activity of greater than 10 moles PMC/mole catalyst, but lessthan 400 moles PMC/mole catalyst. Typically, about 0.5 to 1.0 molarpercent of the catalyst is used, and more preferably about 0.6 to 0.8molar percent based on the phenol fed into the reaction. The catalyst istypically fed into one or more components of the reaction mixture beforeintroduction into the distillation column, but it may be introduced intothe column separately, before or during addition of the reactionmixture. The column may be kept under an inert atmosphere and may bepre-dried if desired.

As shown in the examples, the method according to the present inventionis capable of producing very high yields. Under preferred conditions,the method may be used to produce a total yield of aryl alkyl carbonateplus diaryl carbonate of at least 40%, and optimally at least 50%. Also,the method is capable of producing total yields of diaryl carbonatesversus total diaryl carbonates and arylakyl carbonates of greater than25%, or more preferably 30%, or even 40%.

In order to achieve such high yields in a single column, the conditionswithin the distillation column must be carefully controlled.Specifically, the conditions for reacting DMC and phenol to make DMC andDPC should satisfy requirements (1) and (2) below.

(1) The catalyst should have a catalytic activity such that PMC isproduced at a rate of 40 moles PMC per mole of catalyst wherein thereaction temperature is 210° C., the dialkyl carbonate is dimethylcarbonate, the aromatic hydroxy compound is phenol and the dimethylcarbonate/phenol ratio equals 3.2 (kg/kg) in the reaction system. In thecase of Ti(OPh)_(4,) the optimum molar percent of catalyst is 0.7 basedon the amount of phenol used. For systems using different reactants,optimum factors can be determined by repeating the experiments describedin the Examples below, and by analyzing the data as shown herein.

(2) The reaction should be conducted under conditions satisfying thefollowing relational expressions:

a) PMC+DPC yield (%)=

−197.5−40.9* c+4.07*r+19.4*P

−0.930*T−15.6*c²+2.58*c*r

−0.294*c*T−0.085*P*T

where c is the concentration of catalyst in molar percent based onhydroxy compound, r is the ratio of DMC flow rate (g/h) to phenol feedflow rate (g/h), P is the column pressure (in kg/cm2 Gauge) and T is thereaction temperature (in ° C.). FIG. 3 shows this relation for differentDMC to phenol flow ratios and reaction temperatures at constant catalystamount (0.7 mol %) and constant pressure (4.6 kg/cm2 Gauge). The targetis a PMC+DPC yield greater or equal than 50%. As shown in FIG. 3, thistarget requires that reaction temperatures are higher than 220° C. andDMC to phenol feed flow ratios greater than 4 to 5.

b) Anisole selectivity(%)=

119.4−4.10*c+2.59*r−1.13*T

+0.003*T² 0.143*c*r

+0.023*c*T−0.011*r*T

FIG. 4 shows this relation for different DMC to phenol flow ratios andreaction temperatures and at constant catalyst amount (0.7 mol %). Thetarget anisole selectivity is less than or equal to 0.50%. As can beseen in FIG. 4, this target requires that reaction temperatures be lessthan 230 to 235° C., and that DMC to phenol feed flow ratios are higherthan 4 to 5 (especially at high temperatures).

c) DPC selectivity versus PMC+DPC yield=

−237.5−84.9*c+1.32*r+19.5*P

+1.18*T−12.98*c²+3.37*c*r

+0.403*c*T−0.098*P*T

FIG. 5 shows this relation for different DMC to phenol flow ratios andreaction temperatures at constant catalyst amount (0.7 mol %) andconstant pressure (4.6 kg/cm2 Gauge). The target is to maximize DPCyield versus PMC+DPC yield. It follows from FIG. 5 that maximum DPCyield versus PMC+DPC yield is obtained at high reaction temperatures andhigh DMC to phenol feed flow ratios.

Analysis of the above relational expressions reveals the followingoptimal operation conditions for the reaction of DMC and Phenol to formDPC and PMC:

The amount of catalyst (c): should be 0.5 to 1.0 molar percent,preferably 0.6 to 0.8 molar percent;

The column pressure (P):3 to 6 kg/cm² Gauge, preferably 4 to 5 kg/cm²Gauge;

The reflux ratio should be between 0.2 and 3, preferably between 0.4 and1.0;

The reaction temperature and DMC to phenol feed flow ratio are chosenaccording to the shaded region in FIG. 6. This region denotes thecompilation of reaction temperatures and DMC to phenol feed flow ratiosthat result in a total yield of PMC and DPC of 50% or higher and inselectivity”s to anisole of 0.5% or less. The shaded region of FIG. 6was obtained after determining the overlap of total yield of PMC and DPCof 50% or more from FIG. 3, with anisole selectivity”s of 0.5% or lessfrom FIG. 4. It follows that the marked region consists of reactiontemperatures between 220 and 235° C. and DMC to phenol feed flow ratiosbetween 4 and 6. Remarkably, the marked region is also the region inwhich DPC selectivity relative to the total yield of PMC and DPC ishigh: between 30 and 45%, as shown in FIG. 5. Therefore, this region isa truly optimum region that meets the targets of maximizing yield andminimizing by-product formation. Without wishing to limit the inventionto any single theory of operation, the reason for the high DPC yieldversus PMC+DPC yield is thought to be the combination of hightemperature and low to medium pressure. These two conditions result inlow concentrations of DMC in the reactor mixture (DMC is a low boilingcomponent) and high concentrations of PMC, so the disproportionationreaction of PMC to DPC and DMC is shifted towards the DPC side.

The present invention is further illustrated in a number of workingexamples, summarized in Table 1.

TABLE 1 Feed system Reaction conditions DMC-to- Catalyst Catalyst vsTemp. at DMC Phenol Phenol (**) phenol Pressure bottom Reflux Nr (g/h)(g/h) (g/g) (g/h) (mole-%) (kg/cm²G) (° C.) ratio 1 1741 548 3.18 42.70.70 4.6 210 0.64 2 1739 549 3.17 42.7 0.70 4.6 210 0.64 3 1753 558 3.1457.3 0.93 4.6 210 0.46 4 1820 546 3.33 39.3 0.65 4.6 210 0.69 5 1973 4204.70 29.9 0.64 4.6 237 0.55 6 1890 403 4.69 26.9 0.60 4.6 237 0.57 71474 780 1.89 128.0 1.48 4.6 210 0.60 8 1880 417 4.51 76.1 1.65 4.6 2100.81 9 1880 417 4.51 76.1 1.65 4.6 240 0.32 10 1899 400 4.74 72.9 1.644.6 240 0.31 11 1478 777 1.90 128.0 1.49 4.6 240 1.07 12 1485 787 1.8911.1 0.13 4.6 210 1.24 13 1516 784 1.93 10.8 0.12 4.6 232 0.44 14 1940390 4.97 5.7 0.13 4.6 210 0.33 15 1940 433 4.48 6.0 0.13 4.6 228 0.72 161955 438 4.46 6.1 0.13 4.6 210 0.33 17 1940 438 4.43 6.6 0.14 7.2 2101.08 18 1431 823 1.74 11.6 0.13 7.2 240 1.46 19 1426 850 1.68 11.5 0.127.2 210 1.50 20 1809 444 4.08 6.3 0.13 7.2 239 0.41 21 1808 420 4.3176.1 1.64 7.2 210 0.49 22 1401 768 1.82 143.0 1.68 7.2 240 0.62 23 1418801 1.77 131.4 1.48 7.2 210 2.53 24 1830 402 4.55 76.2 1.71 7.2 240 0.9525 1885 309 6.09 22.7 0.66 4.6 231 0.47 26 1720 401 4.29 28.8 0.65 4.6231 0.51 27 1876 356 5.27 26.1 0.66 4.6 227 0.47 28 1879 395 4.75 30.80.70 4.6 220 0.49 29 1884 369 5.10 20.9 0.51 4.6 227 0.47 30 1877 3076.12 23.5 0.69 4.6 220 0.47 31 1889 365 5.18 25.2 0.62 4.6 226 0.46 322303 451 5.10 33.6 0.67 4.6 220 0.50 Results bottom product (*)Performance (***) Bottom PMC + DPC DPC yield/ Anisole flowrate PMC DPCAnisole yield PMC + DMC yield selectivity Nr (g/h) (wt-%) (wt-%) (wt-%)(%) (%) (%) 1 972 24.35 3.47 0.035 29.3 9.1 0.19 2 971 24.26 3.49 0.02229.3 9.5 0.12 3 963 27.13 4.55 0.042 32.2 10.0 0.20 4 948 26.73 4.260.028 32.2 11.0 0.16 5 594 39.30 21.25 0.075 57.9 40.5 0.84 6 565 40.0422.19 0.039 59.1 41.2 0.99 7 1483 18.09 1.81 0.032 17.8 −19.2 0.35 8 83126.27 4.01 0.040 32.5 0.4 0.22 9 682 40.11 22.62 0.152 66.1 38.6 0.41 10607 42.12 28.24 0.168 70.0 43.6 1.83 11 1233 27.75 10.28 0.240 35.4 23.11.05 12 1287 16.09 1.43 0.001 17.9 8.9 0.01 13 1083 21.86 5.65 0.08525.0 25.3 0.47 14 692 22.73 2.84 0.041 29.0 14.0 0.26 15 639 26.74 6.370.033 32.1 23.9 0.14 16 733 23.72 3.01 0.051 28.4 13.5 0.27 17 104319.08 1.25 0.043 30.1 6.7 0.36 18 1282 22.84 3.85 0.232 26.8 17.8 1.3919 1885 12.25 0.50 0.001 17.3 2.7 0.01 20 718 32.99 8.78 0.158 44.8 26.40.56 21 1002 24.21 2.55 0.160 35.3 −1.3 1.25 22 1384 26.82 6.62 0.49834.9 14.3 3.11 23 1780 16.73 1.16 0.042 19.9 −15.6 0.53 24 774 37.5712.91 0.314 60.8 26.3 0.97 25 474 41.03 22.21 0.067 66.1 41.2 0.09 26564 37.59 18.12 0.100 52.4 37.6 0.21 27 530 38.18 14.76 0.049 52.2 32.60.10 28 649 33.81 9.57 0.039 45.6 24.7 0.11 29 539 37.91 15.15 0.05651.2 33.1 0.11 30 484 37.20 11.66 0.039 50.0 27.3 0.09 31 534 37.5714.50 0.063 50.2 32.3 0.13 32 717 34.22 10.62 0.045 46.0 26.9 0.12 (*)Top product consists only of DMC (90-95 wt-%) and methanol (5-10 wt-%)(**) Catalyst consists of 40.3 wt-% od litanium tetraphenolate, 36.5 wt% DPC and 23.2 wt % Heavies (***) PMC yield = moles PMC generated permole phenol in feed. DPC yield = moles DPC generated times 2 per molephenol in feed, PMC + DPC yield = PMC yield plus DPC yield Anidoleselectivity − moles anisole generated per mole phenol converted

EXAMPLE 1

A pilot distillation column (stainless steel) as shown in FIG. 2 wasequipped with 40 perforated plates. The plate diameters were 50 mm forthe bottom 20 trays and 40 mm for the top 20 trays. The total height ofthe column was 3.4 m, with a plate-to-plate distance of 50 mm for thebottom 20 trays and 40 mm for the top 20 trays. The holdup of the bottom20 trays was 471 ml of liquid, the holdup of the bottom compartment ofthe column was 460 ml. Heat was supplied at the bottom of the column andto the bottom 20 trays of the column by means of electric heatingmantles. The phenol feed (548 g/h) and catalyst feed (Titaniumtetraphenolate (40.3 wt−%) dissolved in a mixture of DPC (36.5 wt−%) andheavies (23.2 wt−%), flow rate is 42.7 g/h) were mixed (resulting in acatalyst percentage of 0.70 mole−% versus phenol), preheated to 145° C.and then fed to tray 20 of the column. DMC (1741 g/h) was preheated to145° C. and fed to the bottom compartment of the column below the firsttray. The column was operated at a temperature of 210° C. at the bottomof the column, at a pressure of 4.6 kg/cm² Gauge measured at the top ofthe column, and with a reflux ratio of 0.64. The overhead was cooled to90° C. in a condenser and part of the overhead was sent back as refluxto the top of the column. To compensate for heat losses to theenvironment, the bottom 20 trays were heated such that tray 7 (countingfrom the bottom tray) was kept at 5° C. below the bottom temperature andtray 12 (counting from the bottom tray) was kept at 10° C. below thebottom temperature. Table 1 shows the bottom flow rate and bottom flowcomposition under steady state conditions. Table 1 also includes thePMC+DPC yield, the DPC yield relative to the PMC+DPC yield and theselectivity for anisole. The top stream always consisted of DMC andmethanol and is not included in the Table 1.

EXAMPLES 2 TO 32

Using the same apparatus described in Example 1, experiments werecarried out under the reaction conditions indicated in Table 1. Resultsare shown in Table 1. Examples 25 to 32 correspond to preferredconditions according to the present invention.

EXAMPLE 33

The results shown in Table 1 were analyzed and fitted into a model usinga “Custom Response Surface Design” from the software package Minitab ®for Windows, Release 12.2. The commercially available software operatesby using a response surface method to determine the relationship betweenone or more response variables (for instance Yield or Selectivity) and aset of quantitative experimental variables or factors (for instanceTemperature, Pressure, reactant concentrations, etc.). The experimentaldata are fitted into a model. The type of model is chosen by the user.For instance, the user can choose a linear or a quadratic model. Thefitting itself is done via a Least Squares method. The computationalmethod is Givens transformations using Linpack routines. The method isdescribed in: Linpack (1979), Linpack User's Guide by J. J. Dongarra, J.R. Bunch, C. B. Moler, and G. W. Stewart, Society for Industrial andApplied Mathematics, Philadelphia, Pa., which is incorporated byreference herein. Other known curve fitting methods could also be used.

Although the present invention has been described in considerable detailwith reference to certain preferred versions thereof, other versions arepossible. For example, the reaction could be conducted in a type ofreactor other than a distillation column. Alternatively, the reactioncould be conducted in a reaction column connected to a distillationcolumn. Also, the reaction could be conducted using a fixed catalyst bedrather than using a homogeneous catalysts. Also, many other variationsare possible. Therefore, the spirit and scope of the appended claimsshould not be limited to the description of the preferred versionscontained herein.

What is claimed is:
 1. A method for the continuous manufacturing ofaromatic carbonates comprising providing a single distillation columncomprising a lower reactive section having a top and bottom subsection,and an upper rectification section having a top subsection; feeding tothe top subsection of the reactive section a first stream comprising anaryl alcohol and a catalyst; feeding to the bottom subsection of thereactive section a second stream containing a dialkylcarbonate, whereinthe first and second streams are fed in sufficient quantities such thatthe weight ratio between the dialkyl carbonate and aryl alcohol fed intothe distillation column is between 4 and 6, and a temperature at thebottom of the column is between 220° C. and 240° C., wherein anoperating pressure of the column measured at the top of the column isfrom 3 to 6 kg/cm² Gauge, and wherein the reaction is carried out in thepresence of a catalyst based on alkoxides or aryl oxides of titanium,wherein said catalyst is present in a quantity of from 0.5 to 1.0 molarpercent based on the aryl alcohol.
 2. The method according to claim 1,wherein a column reflux ratio is between 0.2 and
 3. 3. The methodaccording to claim 1, wherein the lower reactive section comprises atleast 3 theoretical distillation steps, and the upper rectificationsection comprises at least 3 theoretical distillation steps.
 4. Themethod according to claim 1, wherein a temperature measured at the topof the column is between 110° C. and 210° C.
 5. The method according toclaim 1, wherein the aryl alcohol is phenol, and the dialkylcarbonate isdimethyl carbonate.
 6. The method according to claim 5, wherein a weightratio between dimethylcarbonate and phenol fed into the distillationcolumn is from 4.5 to
 6. 7. The method according to claim 6, wherein thetemperature at the bottom of the column is from 225° C. to 235° C. 8.The method according to claim 7, wherein the catalyst is titaniumtetraphenolate.
 9. The method according to claim 8, wherein the catalystis present in a quantity from 0.6 to 0.8 molar percent based on phenol.